The present disclosure is directed to an apparatus and a method that shape irradiation profile using optical elements having positive and negative optical powers.
Many applications of irradiated energy require depositing energy irradiation, having specific profiles, on a target. The use of electromagnetic energy produced by lasers, of various kinds, is currently ubiquitous. By way of example, lasers, as sources of energy to be deposited on materials, are used in applications in the areas of laser heat processing, cutting, marking, photolithography, and fiber injection.
Quite often, applications that deposit energy on a target require the energy irradiance be substantially uniform on the target over a specified area and at a fixed longitudinal distance from the source. Quite often, also, one does not have exact control on energy beam modes of the laser or other emissive device (e.g., the modes may be unknown, there may be several of them, or they may change in time), beam collimation may not be feasible, or sufficiently achievable, or the source of energy may produce highly irregular irradiance distributions. Among sources of energy having the mentioned characteristics are excimer lasers (as well as other multimode laser beams), laser diode arrays, and arc sources.
In optics, the term xe2x80x9caperturexe2x80x9d refers to an optically active region. For example, in a refractive element (e.g., a lens), the aperture is the area allowing the transmission of the incident irradiation through the optical element; in a reflective optical element (e.g., a mirror), the aperture is the area allowing reflection of the incident radiation; and in a diffractive optical element (e.g., Fresnel lens), the aperture is the area producing the diffracted irradiation from the incident irradiation.
Multi-aperture beam integration is an especially suitable technique for resolving the above-mentioned disadvantages of using energy sources wherein one does not have control on collimation, irradiance, or mode. Multi-aperture integrator systems basically consist of two components; 1) a subaperture array component consisting of one or more apertures (segmenting the entrance pupil or cross section of the beam into an array of beamlets), and 2) a beam integrator or focusing component (overlapping the beamlets from each subaperture at the target plane). A target is located at the focal point of the primary focusing element, where the chief rays of each subaperture intersect. Thus, the amplitude of the irradiance distribution on the target is a Fourier transform of the incoming wavefront modified by the lenslet array. The elements used in these systems have been refractive, reflective, or diffractive. Generally, all known multi-aperture integration systems use aperture elements that have the same shape and phase function.
Multi-aperture beam integrating techniques, however, require attention to obtaining efficient fill-factors lest they direct away a significant amount of available energy from a target. Consequently, the implementations have generally been limited to the stacking of apertures having square, rectangular, and hexagonal shapes because stacking of these aperture shapes provide nearly 100% fill factor at the aperture array. For example, U.S. Pat. No. 5,251,067 to Kamon describes achieving uniform illumination using a fly-eye lens device and system having an array of squares of different sizes. Pepler, et al [hereinafter Pepler] in an article titled xe2x80x9cBinary-phase Fresnel zone plate arrays for high-power laser beam smoothingxe2x80x9d (SPIE Vol. 2404, pages 258-265, 1995) describe facilitating the generation of uniform xe2x80x9ctop-hatxe2x80x9d intensity profiles and spatially shaped foci using Fresnel binary phase zone plate arrays that have square, rectangular, and hexagonal apertures.
Quite a few applications depositing energy on a target, however, have target shapes not limited to squares, rectangles, and hexagons. The near field pattern of a square, rectangle, and hexagon is of the same typexe2x80x94namely, square, rectangle, and hexagon, respectively. For applications requiring target illumination not limited to these shapes, therefore, currently used multi-aperture beam integrating systems do not efficiently deposit predetermined desired energy patterns on the target.
It is the objective of this invention to provide efficient energy deposition on targets having arbitrary shapes. It is also the objective of this invention to shape the irradiation profile on a target to arbitrary yet specific target shapes.
The invention realizes these and other objectives using an arrangement having an array of at least three apertures, an array of optical elements (each aperture being associated with one optical element), wherein at least one aperture (along with the optical element with which the aperture is associated) has a positive optical power and at least one aperture (along with the optical element with which the aperture is associated) has a negative optical power. Positive and negative optical powers cause wavefronts of incident irradiation to converge and diverge, respectively, after exposure to the array of apertures. The principles of the invention may be practiced by arranging the apertures in one, two, or three dimensions.
The invention realizes these objectives by further having the shape of the apertures be any one of square, rectangular, and hexagonal. The invention realizes these objectives by having the apertures in the alternative be asymmetric so that a rotation of the aperture shape by 180 degrees around an axis perpendicular to the surface of the aperture yields an inverted aperture shape. The invention realizes these objectives by further having a primary optical element direct the irradiance onto a target. The invention realizes these objectives by having a zooming optical combination as the primary optical element.